The present invention relates to a conjugated diene block polymer, and more particularly a block polymer of a conjugated diene compound composed of blocks where the modes of microstructure are different from each other.
Hitherto, many kinds of conjugated diene polymers are known, and in particular, isoprene polymers and butadiene polymers prepared by using the so-called Ziegler catalyst and butadiene polymers prepared by using an organolithium catalyst have been used as synthetic rubbers for various purposes. These polymers are characterized by their modes of microstructure. In general, it is known that they are polymers having a high cis content or a high cis and trans content. These polymers, particularly in case of applying to the use as tires for automobiles, have a feature that dynamic heat generation is a little. However, they have a drawback that the braking characteristics which are another important performance required in tires are bad, and in particular are remarkably lacking in the wet skid resistance which indicates the braking characteristic on a wet road. In order to cover up the drawback, there has been adopted, for instance, a manner using a rubber blend in which a styrene-butadiene rubber is incorporated in a suitable proportion. This manner improves the wet skid resistance, but increases the dynamic heat generation, thus resulting in increase of the rolling resistance of tires. It is the present condition in this industry that a rubber composition indicating such unsatisfactory characteristics is employed.
On the other hand, in recent years, it has been found, as disclosed in Japanese Patent Publication No. 20771/1973, that a rubber composition containing a conjugated diene polymer having a high content of 1,2-bonding provides a product having characteristic mechanical properties such as high impact resilience, high breaking strength and excellent low temperature resistance. Such a rubber composition is suitable as a material for tires of passenger cars, etc. In particular, it is expected that a rubber composition containing a polybutadiene having a high 1,2-bonding content would provide an excellent material for tires in that both characteristics of the wet skid resistance and the dynamic heat generation could be improved together. However, no reports on the influences of the polymer structure such as the content or distribution of such 1,2-bonding in a polymer have been made, and the optimization thereof has been demanded. In the present age where improvement of the braking characteristics or the wet skid resistance is demanded, particularly for ensuring safety with development of a superhighway system, and on the other hand, reduction of the dynamic heat generation or rolling resistance of tires is demanded due to a rise of energy cost, it is a very important subject to improve the both characteristics together.